[ash-md] Implements a shadow over overview items and selector

ui/wm/core/shadow.h

Index: ui/wm/core/shadow.h
diff --git a/ui/wm/core/shadow.h b/ui/wm/core/shadow.h
index 813e7a907f1632f16f5a51126b8d618a39d7570b..81199f848fd361d94cbc7ac006e66935f0f8ec22 100644
--- a/ui/wm/core/shadow.h
+++ b/ui/wm/core/shadow.h
@@ -45,6 +45,10 @@ class WM_EXPORT Shadow : public ui::ImplicitAnimationObserver {
   // transformations to this layer).
   ui::Layer* layer() const { return layer_.get(); }
 
+  // Exposed to allow setting animation parameters for bounds and opacity
+  // animations.
+  ui::Layer* shadow_layer() const { return shadow_layer_.get(); }
+
   const gfx::Rect& content_bounds() const { return content_bounds_; }
   Style style() const { return style_; }